She has been a columnist for The Wall Street Journal, The Atlantic, The New York Times, and Forbes and its companion technology magazine Forbes ASAP.

From July 1989 to January 2000, Postrel was the editor of Reason magazine. Under her leadership, Reason was a finalist for the National Magazine Awards, the industry's highest honor, for essays in 1993 and public interest journalism in 1996 and in 1998, when Reason had two finalist articles. She founded Reason.com in 1995, establishing Reason as an online pioneer.

Prior to becoming editor of the magazine in 1989, Postrel served as associate editor of Reason and, before that, as a reporter for Inc. and The Wall Street Journal.